#Single transistor fm transmitter how to

Therefore, by changing the base current you change the frequency of the oscillation which is how the FM (frequency modulation) signal is produced.Įmitting the FM signal is done by AE1 which is a long piece of wire. By altering the base current these values change as well and since the oscillation in the circuit is dependent on all capacitors and inductors in the LC tank, the parasitic capacitances also affect the frequency of oscillation. Between the base – emitter, base – collector, and collector – base, are parasitic capacitances whose capacitance value depends on the base current. Modulation is achieved thanks to parasitic capacitances inherent in BJT transistors.

#Single transistor fm transmitter how to

This increase in conduction results in C4 discharging and the whole cycle starting all over again. 86 20 Download By CableGuy Follow More by the author: Hello Im gonna show you How to make a Simple FM Transmitter that works with only an AA battery. When this happens the voltage across R2 reduces which increases the size of Vbe and therefore increases the conduction of Q1. As C4 begins to charge the amount of current flowing through C4 reduces which results in less current flowing through R2. This increase in voltage on the emitter therefore results in a smaller value of Vbe and this reduction in Vbe reduces the conduction of Q1. Current flowing through R2 will result in a voltage drop across R2 and since R2 is connected to the emitter of Q1, the same voltage will be present on the emitter of Q1. This rush of current will also pass through C4 via capacitive coupling which will result in current flowing through R2. When power is applied to the circuit, a rush of current flows through the inductor. The oscillator consists of C2, L1, C4 and R2 with the frequency of oscillation being determined by C2 and L1 only. The next stage is the modulation/oscillation stage which provides a carrier signal which is then modulated by the input signal. R1 provides biasing for the transistor by feeding a small amount of current into the base (which prevents the transistor from turning off). C3 is used to couple the input signal so that no DC component is fed into the transmitter.

Input signals into the FM transmitter must not contain a DC component as it would adversely affect the modulation/oscillation stage (by saturating the transistor) and therefore no FM signal would be generated. If you want fixed transmission carrier then calculate FM tank oscillation (L1, C2) and choose the elements. Here Transistor BC547 configured in common emitter and input signal is taken from condenser mic. The input stage consists of capacitors C3 and C1, and resistor R1. This Single Transistor Voice FM Transmitter circuit can produce FM Carrier signal from 50MHz to 160MHz by using the C1 and C2 tank circuit. at 1.5 Volts Main advantage of this circuit is that power supply is a 1.5Volts cell (any size) which makes it possible to fix PCB and the battery into very tight places. The circuit has three main stages, the input stage, the modulation stage, and the output. Schematic Simple FM Transmitter involves on a single transistor oscillator Technical datas: Supply voltage : 1.1 - 3 Volts Power consumption : 1.8 mA at 1.5 Volts Range : 30 meters max.